/*
 * Copyright (C) 2009 The Guava Authors
 *
 * Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except
 * in compliance with the License. You may obtain a copy of the License at
 *
 * http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software distributed under the License
 * is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express
 * or implied. See the License for the specific language governing permissions and limitations under
 * the License.
 */

package com.google.common.escape;

import static com.google.common.base.Preconditions.checkNotNull;

import com.google.common.annotations.Beta;
import com.google.common.annotations.GwtCompatible;
import com.google.common.annotations.VisibleForTesting;

import java.util.Collections;
import java.util.Map;

/**
 * An implementation-specific parameter class suitable for initializing {@link
 * ArrayBasedCharEscaper} or {@link ArrayBasedUnicodeEscaper} instances. This class should be used
 * when more than one escaper is created using the same character replacement mapping to allow the
 * underlying (implementation specific) data structures to be shared.
 *
 * <p>The size of the data structure used by ArrayBasedCharEscaper and ArrayBasedUnicodeEscaper is
 * proportional to the highest valued character that has a replacement. For example a replacement
 * map containing the single character '{@literal \}u1000' will require approximately 16K of memory.
 * As such sharing this data structure between escaper instances is the primary goal of this class.
 *
 * @author David Beaumont
 * @since 15.0
 */
@Beta
@GwtCompatible
@ElementTypesAreNonnullByDefault
public final class ArrayBasedEscaperMap
{
    /**
     * Returns a new ArrayBasedEscaperMap for creating ArrayBasedCharEscaper or
     * ArrayBasedUnicodeEscaper instances.
     *
     * @param replacements a map of characters to their escaped representations
     */
    public static ArrayBasedEscaperMap create(Map<Character, String> replacements)
    {
        return new ArrayBasedEscaperMap(createReplacementArray(replacements));
    }

    // The underlying replacement array we can share between multiple escaper
    // instances.
    private final char[][] replacementArray;

    private ArrayBasedEscaperMap(char[][] replacementArray)
    {
        this.replacementArray = replacementArray;
    }

    // Returns the non-null array of replacements for fast lookup.
    char[][] getReplacementArray()
    {
        return replacementArray;
    }

    // Creates a replacement array from the given map. The returned array is a
    // linear lookup table of replacement character sequences indexed by the
    // original character value.
    @VisibleForTesting
    static char[][] createReplacementArray(Map<Character, String> map)
    {
        checkNotNull(map); // GWT specific check (do not optimize)
        if (map.isEmpty())
        {
            return EMPTY_REPLACEMENT_ARRAY;
        }
        char max = Collections.max(map.keySet());
        char[][] replacements = new char[max + 1][];
        for (Character c : map.keySet())
        {
            replacements[c] = map.get(c).toCharArray();
        }
        return replacements;
    }

    // Immutable empty array for when there are no replacements.
    private static final char[][] EMPTY_REPLACEMENT_ARRAY = new char[0][0];
}
